Head-mounted Optical Coherence Tomography
The invention provides a system and method for obtaining ophthalmic measurements whereby the inventive device is configured to be head mountable, automatically axially length aligned with a selected target, and laterally aligned so that light from an OCT source enters through the pupil of the eye under test. The frame of the head mountable OCT is customizable, capable of analyzing both the left and right eye of a subject. The inventive device can be operated by the person undergoing test. Embodiments include mechanisms for eye fixation, lateral, angular and depth scanning of target regions. A variety of embodiments are taught, including the scanning of both eyes of a subject at substantially the same time, and a configuration of a photonic module coupleable with a plurality of frames. Embodiments include a variety of OCT sources, such as MRO, swept source, time domain, and spectral domain.
This patent application, docket number CI130701PT, is related to U.S. Pat. No. 7,526,329 titled “Multiple Reference Non-invasive Analysis System” and U.S. Pat. No. 7,751,862 titled “Frequency Resolved Imaging System”, the contents of both of which are incorporated herein as if fully set forth herein. This patent application is also related to the following three patent applications, all of which were filed on Nov. 3, 2012: PCT patent application number PCT/US2012/063471 (docket number CI120625) titled “Improved Correlation of Concurrent Non-invasively Acquired Signals”; patent application Ser. No. 13/668,261 (docket number CI121103) titled “A Field of Light based Device”; and patent application Ser. No. 13/668,258 (docket number CI121101) titled “Non-invasive Optical Monitoring”; the contents of all of which are incorporated herein as if fully set forth herein.
FIELD OF THE INVENTIONThe invention described and illustrated in this application relates to non-invasive imaging and analysis techniques such as Optical Coherence Tomography (OCT). In particular it relates the use of OCT systems to make in-vivo measurements of aspects of an eye. Such OCT systems include, but are not limited to, the multiple reference OCT systems, referred to as an MRO system, that is described in U.S. Pat. Nos. 7,751,862 and 7,526,329.
BACKGROUND OF THE INVENTIONNon-invasive imaging and analysis of targets is a valuable technique for acquiring information about systems or targets without undesirable side effects, such as damaging the target or system being analyzed. In the case of analyzing living entities, such as human tissue, undesirable side effects of invasive analysis include the risk of infection along with pain and discomfort associated with the invasive process.
Optical coherence tomography (OCT) is a technology for non-invasive imaging and analysis. There exists more than one OCT technique. Time Domain OCT (TD-OCT) typically uses a broadband optical source with a short coherence length, such as a super-luminescent diode (SLD), to probe and analyze or image a target. Multiple Reference OCT (MRO) is a version of TD-OCT that uses multiple reference signals. Another OCT technique is Fourier Domain OCT (FD-OCT). A version of Fourier Domain OCT, called Swept Source OCT (SS-OCT), typically uses a narrow band laser optical source whose frequency (or wavelength) is swept (or varied) over a broad wavelength range. In TD-OCT systems the bandwidth of the broadband optical source determines the depth resolution. In SS-OCT systems, depth the wavelength range over which the optical source is swept determines the depth resolution. Another variation of FD-OCT is spectral domain where the detection process separates wavelengths by means of a spectrometer.
TD-OCT technology operates by applying probe radiation from the optical source to the target and interferometrically combining back-scattered probe radiation from the target with reference radiation also derived from the optical source. The typical TD-OCT technique involves splitting the output beam into probe and reference beams, typically by means of a beam-splitter, such as a pellicle, a beam-splitter cube, or a fiber coupler. The probe beam is applied to the target. Light or radiation is scattered by the target, some of which is back-scattered to form a back-scattered probe beam, herein referred to as signal radiation.
The reference beam is typically reflected back to the beam-splitter by a mirror. Light scattered back from the target is combined with the reference beam, also referred to as reference radiation, by the beam-splitter to form co-propagating reference radiation and signal radiation. Because of the short coherence length, only light that is scattered from a depth within the target whose optical path length is substantially equal to the path length to the reference mirror can generate a meaningful interferometric signal.
Thus the interferometric signal provides a measurement of scattering properties at a particular depth within the target. In a conventional TD-OCT system, a measurement of the scattering values at various depths can be determined by varying the magnitude of the reference path length, typically by moving the reference mirror. In this manner the scattering value as a function of depth can be determined, producing a depth scan of the target.
Various techniques exist for varying the magnitude of the reference path length. Electro-mechanical voice coil actuators can have considerable scanning range, however, there are problems with maintaining stability or pointing accuracy of a reference mirror. Fiber based systems using fiber stretchers have speed limitations and have size and polarization issues. Rotating diffraction gratings can run at higher speeds, but are alignment sensitive and have size issues.
Piezo devices can achieve high speed scanning and can have high pointing accuracy, however to achieve a large scanning range requires expensive control systems and such systems have limited speed. A scanning method that effectively amplifies the scan range of a piezo device is described in the U.S. Pat. Nos. 7,526,329 and 7,751,862 referenced hereinabove.
The technique described in these publications uses multiple reference signals with increasing scan range and correspondingly increasing frequency interference signals. This scanning method can achieve large scan range at high speed with good pointing stability. The interference signals associated with the multiple reference signals are detected by a single detector as a complex signal consisting of the combined interference signals.
In swept source Fourier domain OCT systems depth scanning is accomplished by repeatedly sweeping the wavelength of the optical source. The wavelength range over which the optical source is swept determines the depth resolution. The period of the sweep repetition rate determines the period of the depth scans.
In addition to depth scanning, lateral scanning of a target is required for many imaging and analysis applications. Some conventional techniques for lateral scanning use stepper or linear motors to move the OCT scanning system. In some applications angular scanning is accomplished by electro-mechanical oscillating mirrors, typically referred to as galvo-scanners, which angularly deviate the probe beam.
Currently available OCT systems are bulky, weighty, complex and high cost. Currently available OCT systems have complex and bulky alignment and scanning sub-systems that result in physically large and costly systems. Moreover, in typical ophthalmic applications currently available OCT systems must be operated by a trained physician or technician. What is needed is a lightweight, robust, reliable monitoring device that is amenable to alignment by a layperson, and provides reliable and accurate measurements.
Furthermore, ophthalmic applications, such as retinal examination, often require the retina to be at a fixed orientation with respect to the OCT probe beam or with respect to the scanning region of the OCT probe beam. This process is also referred to as “fixation” of the eye. Currently available OCT systems that require fixation at locations other than the location being analyzed by the OCT beam also require a complex fixation mechanism.
Major causes of blindness are macular degeneration and diabetic retinopathy. Both of these conditions can benefit from timely medical intervention. People who are at risk of eye damage from these conditions need frequent monitoring because occurrence of an adverse situation (for example the growth of weak and leaky blood vessels), if not addressed in a timely manner, can cause irreversible damage to the retina leading inexorably to loss of vision.
Current practice involves monthly visits to a doctor. Many of these visits are wasteful if nothing has changed and in the case of a change, significant irreversible damage can occur within a month. Therefore, reducing the time between retinal measurements without being wasteful is advantageous.
In the retina of an eye, both the vascular system and the central nervous system are accessible for non-invasive analysis by an OCT system. This provides the opportunity to monitor for the onset or progression of a myriad of conditions, in addition to macular degeneration and diabetic retinopathy. Frequent monitoring of such conditions would be facilitated by a low cost system capable of making the required measurements without the aid of a trained professional.
There is therefore an unmet need for a low cost OCT system capable of making in-vivo OCT measurements of an eye, where such a system has automatic alignment, scanning and fixation mechanisms that do not need a trained operator and can preferably be operated by the subject him or herself. What is also needed is a system that communicates scan results to a medical professional.
SUMMARY OF THE INVENTIONThe invention taught herein meets at least all of the aforementioned unmet needs. The invention provides a method, apparatus and system that has fixed coarse alignment and automatic fine alignment of an OCT system with respect to an eye. In some embodiments the system also provides a scan of a desired region and uses a flexible fixation technique.
In the preferred embodiment, a photonic module attaches to a frame that fits on a subject's head in a manner that may be similar to a pair of spectacles. The frame is selected such that, when attached to the frame, the photonic module is at least coarsely aligned with at least one of the subject's eyes and such that the OCT scanning region is at least coarsely aligned with the retina of the eye, i.e. is aligned with the axial length of the eye.
In the preferred embodiment the frame includes a turning mirror that directs the OCT beam into the Subject's eye. In alternate embodiments one or more corrective lenses compensate for refractive error of the Subject's eye(s). In further alternate embodiments, the corrective lens is adjustable, either manually or by electronic control. Such adjustable lenses are referred to as configurable corrective lenses.
In the preferred embodiment the photonic module includes a movable component that enables dynamic fine axial length adjustment. This fine axial length adjustment is performed using feedback from the processed OCT depth scans of the retina.
In the preferred embodiment the photonic module can be attached to either side (right or left) of the frame in a manner that coarsely aligns the photonic module with respect to the location of the center of the front of the target eye, and with respect to the axial length of the target eye, and with respect to the refractive error of the target eye. The ability to be attached to either side of the frame enables the system to measure aspects of either eye in turn. Other embodiments enable measuring both of a subject's eyes without moving the module.
In an alternate embodiment, the turning mirror that directs the OCT beam into the Subject's eye is angularly adjustable to enable pointing to a particular locality of the retina or a selected set of localities of the retina or to enable scanning a particular region of the retina of the eye.
In an alternate embodiment, the turning mirror that directs the OCT beam into the Subject's eye is angularly adjustable to enable fixation techniques that facilitate pointing to one or more localities or scanning a particular region of the retina. Fixation techniques include using the OCT probe beam as the fixation signal or using a visible beam at a wavelength different from the wavelength of the OCT probe beam. In a further embodiment the system includes a camera.
The drawings to aid in understanding the invention are:
The invention taught herein includes a device and method of non-invasively measuring aspects of a component of an eye. Such components include, but are not limited to, the retina of an eye. Such aspects include, but are not limited to: the thickness of the retina at a particular location; the thickness of the retina at a set of locations; a depth scan of the retina at one or more locations; a two dimensional scan of a region of the retina where one dimension is depth.
In the preferred embodiment, an OCT photonic module directs a light beam, referred to as a probe beam, into the eye and captures at least a portion of the light that is scattered back towards the OCT photonic module. This back-scattered light is combined with reference light to form one or more interference signals that can be processed to a yield depth scan of the retina.
In the preferred embodiment a frame is configured to fit a particular Subject (or set of subjects) whose eye is the target eye to be measured much in the manner that a pair of spectacles is fitted to a person. The frame is further configured so as to be laterally aligned with the target eye such that the probe beam of the OCT photonic module will be directed into the target eye through its pupil. As used herein, “laterally aligned” refers to aligning in a direction orthogonal to the probe beam entering the eye, also referred to as aligning in a lateral direction.
Note regarding numbering in the Figures: components remaining constant from one Figure to another are, where possible, given the same number as in a preceding Figure. Where the only difference is the addition or substitution of components, only components not previously appearing are numbered and discussed. In cases of the configuration of the OCT photonic module, taking into account that OCT is well understood, it is opined that those of average skill in the relevant art will find the Figures illustrative, and an aid to understanding the invention.
The second component 103, in an alternate embodiment, includes one or two lenses, depicted as a first and a second curved surface 117 and 119 (also referred to herein as “corrective” lenses). Such optional lenses may be convex or concave and are selected to compensate for aberration errors in the target eyes, similar to the manner in which, for example, corrective lenses correct for distance vision. It can be appreciated that in the case where the invention is “customized” for a particular subject or eye patient, inclusion of corrective lenses is an aspect of such customization.
The second component 103 is oriented upon, or, in some embodiments, affixed to the first component 101 such that the two 45 degree mirrors 111 and 113 are in front of and centered on the pupils of the left and right eye of the subject. Thus, the first component 101 and the second component 103 together form a frame 100 that is placed anterior to the eyes of a subject and is aligned with the eyes of the subject, where at least one of the eyes is a target eye to be measured or scanned. It can be appreciated that while the preferred embodiment is an eyeglass-like frame, many versions of head-mounting are envisioned, wherein the positioning of the second component provides for directing of the OCT beams onto the target region of the subject's eye or eyes. For example, if weight is a concern, a helmet like device is an alternate embodiment.
The OCT photonic module 201 includes a source 210 that generates radiation directed by a configuration of lenses, mirrors and beam-splitter to probe radiation 205, making a round-trip along pathway 105 (in
Reference radiation proceeds from the beam-splitter 212 to a first turning mirror 213 along reference path 206 passing through a dispersion compensator 225, a third lens 227 to a fifth turning mirror, a sixth turning mirror 233, to a partial reflective mirror 235, and a reference mirror 237. The embodiment depicted in
As depicted in
As can be seen in
The term “axially length aligned”, for the purposes of this application, means that when an object or a portion of an object—that is to say, a target of interest—is “axially length aligned”, the optical path length from the OCT beam-splitter to the target is substantially equivalent to the optical path length from the OCT beam-splitter to the OCT reference mirror. When these two path lengths are substantially equivalent, the object or portion of the object can be depth scanned by the OCT system. In the present invention, the object of interest is typically an eye, and a portion of the object is typically a component of an eye.
Referring again to
Fine axial length alignment is accomplished by dynamically adjusting an optical path length of the OCT photonic module 201. The dynamically adjusted optical path length is either the optical path length from the OCT beam-splitter 212 to the OCT reference mirror 237 or, alternatively, the OCT beam-splitter 212 to the retina [not shown]. It follows that in cases where the target is not the retina but another component of an eye, the distance is that of the OCT beam-splitter to the target of interest. Such fine alignment is achieved using feedback acquired by processing interference signals acquired by the OCT photonic module and is achieved by adjusting the lateral position of the stage 229. Those skilled in OCT operation and OCT signal processing can appreciate this without more description here. Thus, after fine axial length alignment is achieved, interference signals are acquired by the OCT photonic module and the acquired interference signals are processed to measure an aspect of the eye.
An appropriate selection of distance 407 of
In an embodiment of the invention, as described above, the OCT photonic module can be readily attachable to and detachable from a frame in at least two configurations, such that in a first configuration the OCT photonic module is aligned with a first eye and in a second configuration is aligned with the second eye, i.e. the fellow eye of the first eye.
It can be appreciated that the optional corrective lenses (117 and 119 of
In an alternate embodiment, the OCT photonic module is readily attachable to multiple different frames. In this embodiment, any user customization of corrective lenses would be in the user's frame, not necessarily in the OCT photonic module. In a further embodiment, the OCT photonic module is attached to a frame, and a switch enables measurements to be made on a first and a second eye without re-seating the module.
Referring now to
Many other embodiments are possible. For example,
It can be appreciated that a single unitary device, where the frame and photonic module are fixed as a unit, and the module not easily removable, is also an embodiment of this invention.
Seating the OCT photonic module on the frame is now described with respect to
In the preferred embodiment, such magnetic locating connectors also provide electrical power, one or more data and control signal paths between the OCT photonic module and the frame. The use of two locating magnetic connectors that are asymmetric ensures correct orientation of the OCT photonic module. Additional, stabilizing connectors are depicted as 606 and 608 (with apertures for the light paths). It is should be noted that the element 103, i.e. the light guide or second component as depicted in
It can be appreciated that the connectivity of the frame is configurable to wirelessly connect to a controlling device, such as a smart phone or a computer. The controlling device is configurable by, for example, a downloadable software application, enabling the Subject him or herself to make retinal measurements. Further data and scan results can be up-loaded and transmitted to a medical professional or to a medical file.
The invention also provides for scanning of the target, such as the retina of the eye, using angular adjustment of the mirrors in the frame. Referring again to
In addition, embodiments of the inventive device that include angularly adjustable mirrors provide a useful fixation function. Fixation, for ophthalmic purposes and as used herein, means the directing of an eye towards a fixed point. Fixation is useful in that it enables directing the OCT beam to a selected or targeted location or region of the retina. In this embodiment fixation can be achieved by having the angularly adjustable turning mirror oriented in a first direction to achieve a desired fixation direction for a first time period wherein fixation is achieved by the subject looking at the OCT probe beam and then rapidly switching the angularly adjustable turning mirror to be orientated in a second direction to achieve at least one depth scan at a selected target location that is different from the fixation orientation.
The angularly adjustable turning mirror can be repeatedly switched between the desired fixation direction and at least one target scan location to achieve a measurement at a desired location. The angularly adjustable turning mirror may be repeatedly orientated in a set of directions that form a pattern and fixation can be achieved by having the Subject look at the center of the pattern.
In an alternate embodiment a selected region of the eye is scanned by operating the angularly adjustable turning mirror in a scanning mode. In this embodiment fixation is achieved by the use of an additional visible beam and by intermittently adjusting the angle of the turning mirror such that it is oriented in a desired fixation direction for a first period of time and turning on the visible beam wherein fixation is achieved by the subject looking at the visible beam.
At times other than the first period of time when fixation is achieved, scanning is achieved by systematically angularly adjusting one of the turning mirrors 111 or 113 of
In other embodiments, rather than acquiring interference signals from the retinal region of the eye, aspects of other components of the eye are analyzed. It can be appreciated that the target component to be analyzed includes eye components of interest such as the cornea, the anterior chamber or the crystalline lens the eye. In typical ophthalmic applications, the aspect of the target component to be measured is the thickness of the target component.
The angularly scanning approach is further illustrated in
An alternate embodiment that enables larger scan angles is depicted in
Referring again to
Although the OCT systems illustrated are a multiple reference time domain OCT system and a swept source OCT system, it can be appreciated that alternate embodiments use other OCT systems such as conventional time domain OCT systems and spectral Fourier domain OCT systems. In some embodiments an OCT system external to the photonic module could be fiber coupled to the photonic module. This arrangement enables availing of the advantages of the low cost custom frame while using expensive very high performance OCT systems.
An alternate embodiment is depicted in
The photonic module illustrated uses a single OCT beam. In alternate embodiments, the invention includes an array of SLDs (super luminescent diodes) or, alternatively, a single high power SLD, is used and separated into multiple beams by means of a holographic optical element. The resulting multiple beams are directable at different angles so as to probe different locations on the retina. The resulting multiple interference signals are focusable onto a detector array by means of a lens array, providing a set of depth scans at an array of locations simultaneously. This effectively enables measurements to be made in less time.
Other examples will be apparent to persons skilled in the art. The scope of this invention is determined by reference to the specification, the drawings and the appended claims, along with the full scope of equivalents as applied thereto.
Claims
1. A device, said device comprising:
- a frame, a User-customizable unit, and an optical coherence tomography system, where said frame is mountable on a User head, said head having at least one eye to be tested, so that said optical coherent tomography system and said User-customizable unit, mounted on said frame permits probe radiation to enter said eye under test, and a light emitting diode which is on and off for predetermined durations, and wherein light from said light emitting diode is collimated and combined and made collinear with said probe beam by means of a dichroic mirror, and wherein a turning mirror is in the optical path and positioned in a first position relative to said eye under test, wherein said turning mirror is oriented for fixation in a preselected direction when mirror is in said first position and, once in position, said light emitting diode is turned on, and, once the light emitting diode is off, and said turning mirror is oriented in a second position, to direct said probe beam to obtain a scan of a desired target region,
- wherein, said turning mirror switches between two positions, a first position when said light emitting diode is on and fixation is performed, and a second position, said second position comprising a range of positions so as to accomplish as area scan, and
- wherein said mirror repeatedly assumes said first position, and fixation is achieved, and repeatedly assumes at least one second position where scanning is achieved.
2. A method of measuring thickness of a selected portion of an eye under test, said method comprising the steps of:
- using an optical coherent tomography system mounted on a wearable frame, wherein light from a light emitting diode is collimated and combined and made collinear with said optical coherence tomography probe beam by means of a dichroic mirror;
- positioning a turning mirror in the optical path in a first position relative to said eye under test, wherein said first position is oriented for fixation in a preselected direction and when in said first position said light emitting diode is switched on; and
- positioning said turning mirror, and the light emitting diode is off, in a second position to direct said probe beam to obtain a scan of a desired target region,
- wherein the step of directing said probe beam from said second position further includes a range of positions so as to accomplish as area scan, and
- wherein the step of said mirror assuming a first position is performed repeatedly, and the step of assuming at least one second position is performed repeatedly.
Type: Application
Filed: Dec 23, 2019
Publication Date: Jun 18, 2020
Inventor: Joshua Noel Hogan (Los Altos, CA)
Application Number: 16/724,795